The present invention pertains to azeotropic and azeotrope-like compositions of 1,1,1,3,3-pentafluoropropane and 1-chloro-1,1,3,3,3-pentafluoropropane. The compositions of the invention find use not only as intermediates in the production of 1,1,1,3,3-pentafluoropropane, but they are additionally useful as refrigerants, blowing agents and solvents.
In recent years there has been universal concern that completely halogenated chlorofluorocarbons (CFC""s) might be detrimental to the Earth""s ozone layer. Consequently, there is a worldwide effort to use fluorine-substituted hydrocarbons which contain fewer or no chlorine substituents. In this regard, 1,1,1,3,3-pentafluoropropane (HFC-245fa), a hydrofluorocarbon having zero ozone depletion potential, is being considered as a replacement for chlorofluorocarbons such as dichlorodifluoromethane in refrigeration systems and trichlorofluoromethane as a blowing agent. The production of HFC""s, i.e. compounds containing only carbon, hydrogen and fluorine has been the subject of interest to provide environmentally desirable products for use as solvents, blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing compositions and power cycle working fluids. It is known in the art to produce fluorocarbons such as HFC""s by reacting hydrogen fluoride with various hydrochlorocarbon compounds.
HFC-245fa is well known in the art and may be prepared according to the process described in U.S. Pat. No. 5,574,192, herein incorporated by reference in its entirety.
It has now been found that an important intermediate in the production of substantially pure HFC-245fa, is an azeotrope or azeotrope-like mixture of 1,1,1,3,3-pentafluoropropane and 1-chloro-1,1,3,3,3-pentafluoropropane (HCFC-235fa). This intermediate, once formed, may thereafter be separated into its component parts by extraction techniques or pressure swing distillation, even though they have close boiling points. HFC-245fa and HCFC-23 5fa have boiling points of has a boiling point of 15.1xc2x0 C. and 27.57xc2x0 C., respectively at 745.8 mmHg. Alternatively, the HCFC-235fa may be converted to a more highly fluorinated hydrofluorocarbon such as 1,1,1,3,3,3-hexafluoropropane (HFC-236fa), which may be separated from HFC-245fa by conventional means.
In one embodiment, the invention provides azeotropic or azeotrope-like compositions comprising effective amounts of 1,1,1,3,3-pentafluoropropane and 1-chloro-1,1,3,3,3-pentafluoropropane. By xe2x80x9ceffective amountsxe2x80x9d is meant the amount of each component that, on combination with the other component, results in the formation of an azeotropic or azeotrope-like composition.
An azeotropic composition consisting essentially of 1,1,1,3,3-pentafluoropropane and 1-chloro-1,1,3,3,3-pentafluoropropane has been found to have a boiling point of about 14.95xc2x0 C. at a pressure of from about 0 and about 60 psig. At a pressure of about 0 psig the azeotropic composition contains about 650 ppm 1-chloro-1,1,3,3,3-pentafluoropropane. At a pressure of about 10 psig the azeotropic composition contains about 23 ppm 1-chloro-1,1,3,3,3-pentafluoropropane.
The azeotrope-like compositions of the invention consist essentially of greater than 0 to about 50 weight percent 1-chloro-1,1,3,3,3-pentafluoropropane and about 50 to less than 100 weight percent 1, ,1 ,3,3-pentafluoropropane. In a preferred embodiment, the invention provides azeotrope-like compositions consisting essentially of about 1 weight percent 1-chloro-1,1,3,3,3-pentafluoropropane and about 99 weight percent 1,1,1,3,3-pentafluoropropane. The azeotrope-like compositions of the invention have boiling points of about 14.95xc2x10.15xc2x0 C. at a pressure of about 746 mmHg.
In another embodiment, the present invention provides a process for separating 1,1,1,3,3-pentafluoropropane from an azeotropic or azeotrope-like mixture of 1,1,1,3,3-pentafluoropropane and 1-chloro-1,1,3,3,3-pentafluoropropane, which process comprises, consists essentially of, or consists of the steps of:
(A) distilling a mixture comprising, consisting essentially of, or consisting of at least an azeotropic mixture of 1,1,1,3,3-pentafluoropropane and 1-chloro-1,1,3,3,3-pentafluoropropane at a first pressure to produce a first overhead stream enriched in either the 1,1,1,3,3-pentafluoropropane or 1-chloro-1,1,3,3,3-pentafluoropropane and a first bottoms stream enriched in the other component; and
(B) redistilling the first overhead stream at a second pressure to produce a second overhead stream enriched in the component enriched in the first bottoms stream and a second bottoms stream enriched in the component enriched in the first overhead stream.